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7.3.13 Helper functions for UDP connections

The UDP helper functions abstract away UDP connection handling from the other examples. It is required to build the examples using UDP.

/* This example code is placed in the public domain. */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>

/* udp.c */
int udp_connect(void);
void udp_close(int sd);

/* Connects to the peer and returns a socket
 * descriptor.
extern int udp_connect(void)
	const char *PORT = "5557";
	const char *SERVER = "";
	int err, sd;
#if defined(IP_DONTFRAG) || defined(IP_MTU_DISCOVER)
	int optval;
	struct sockaddr_in sa;

	/* connects to server
	sd = socket(AF_INET, SOCK_DGRAM, 0);

	memset(&sa, '\0', sizeof(sa));
	sa.sin_family = AF_INET;
	sa.sin_port = htons(atoi(PORT));
	inet_pton(AF_INET, SERVER, &sa.sin_addr);

#if defined(IP_DONTFRAG)
	optval = 1;
	setsockopt(sd, IPPROTO_IP, IP_DONTFRAG, (const void *)&optval,
#elif defined(IP_MTU_DISCOVER)
	optval = IP_PMTUDISC_DO;
	setsockopt(sd, IPPROTO_IP, IP_MTU_DISCOVER, (const void *)&optval,

	err = connect(sd, (struct sockaddr *)&sa, sizeof(sa));
	if (err < 0) {
		fprintf(stderr, "Connect error\n");

	return sd;

/* closes the given socket descriptor.
extern void udp_close(int sd)